Diclofenac is a non-steroidal anti-inflammatory drug (NSAID), in the same class of medicine as ibuprofen. It is unclear, from the information provided, why it was prescribed. You should ask your doctor about the rationale.
What you describe sounds like chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis, due to cigarette smoking. The coughing and wheezing may persist for months or even years. But, your decision to quit smoking is extremely important. We would urge you to stick with it, no matter what.
In the meantime, you should be treated with respiratory medicines for COPD/asthma, which are capable of providing good relief of the wheezing and difficulty breathing. Such medicines might include Spiriva® HandiHaler® (tiotropium bromide inhalation powder), a long-acting inhaled bronchodilator such as Serevent, ® Inhalation Aerosol (salmeterol xinafoate) a short-acting "rescue medicine" such as albuterol, and an inhaled steroid, such as Flovent® Inhalation Aerosol (fluticasone propionate). Another option is Advair® (fluticasone propionate and salmeterol), which is a combination of Serevent® Inhalation Aerosol (salmeterol xinafoate) and Flovent® Inhalation Aerosol (fluticasone propionate).
Good luck.